In a development apparatus of a nonmagnetic one-component development system, a developing roller and each member of a photoreceptor drum, a feed roller, and a toner regulating blade are rubbed through a toner layer during operation of the development apparatus. The toner is charged by electrostatic friction at the developing roll and the toner regulating blade, and transferred to an electrostatic latent image formed on the surface of the photoreceptor, and development is performed.
In order to stably feed the toner to the surface of the photoreceptor, the developing roll rotates at a higher speed than the photoreceptor to form images. In this case, distortion occurs between the developing roll and contact members in pressure contact with the developing roll. When the distortion is removed, stick slip (vibration) occurs.
Accordingly, the nip width between the photoreceptor and the developing roll changes, and the amount of toner fed to the electrostatic latent image changes. Further, vibration and rotation unevenness by gears of the developing roll, photoreceptor, etc., cause stick slip, transfer of the toner from the developing roll onto the photoreceptor changes, and banding (horizontal stripes) of a constant period occurs in the printed image.
For the occurring stick slip, changes in the contact area by stick slip are reduced by releasing the vibration of the constituent material of each member in the development apparatus, and improving driving members (gears); thus, improvements are made for banding.
Regarding developing rollers, the following prior arts have been proposed.
Patent Document 1 proposes a developing roller having a shaft core body and at least one resin layer provided around the shaft core body, wherein the outermost layer of the developing roller comprises a polyurethane resin (A) as a binding resin and polyurethane resin particles (B) dispersed in the polyurethane resin. For distortion generated between the developing roller and the contact member during rotation, the loss tangent of a second layer configured to have a two-layer structure is set within a fixed range, whereby recovery from deformation is slowed down to suppress rotation unevenness, thereby forming stable images.
Patent Document 2 makes the same proposal by forming the second layer from butyl rubber.
Patent Document 3 proposes a developing roller comprising a conductive shaft, an elastomer layer provided on the outer peripheral surface of the shaft, and a surface layer, wherein the elastomer layer contains spherical silica particles, and the spherical silica particles are unevenly distributed so that they are contained in large amounts on the interface side with the surface layer at the axial both ends of the developing roller. Because the spherical silica particles in the elastomer layer are thus unevenly distributed, gaps are formed between the spherical silica particles, and an increase in stick slip is suppressed. Moreover, because regions that contain a large amount of spherical silica particles are present at the ends of the developing roll, toner deterioration is suppressed, and the occurrence of banding is suppressed.
However, the causes for expressing banding include, in addition to rotation unevenness with peripheral members, clearance between the gears of each member, and influence of stick slip caused by abrasion. These may cause banding.
The present applicants have proposed a rubber member for coating a developing roll obtained by curing a coating layer component around a developing roll; wherein the coating layer component comprises (A) a liquid binder comprising a polyol, an isocyanate compound and a reactive silicone oil, (B) specific silicone rubber particles, and (C) a diluting solvent and the ratio of the rubber particle diameter to the thickness of the coating layer after curing (rubber particle diameter/coating layer thickness) satisfies <0.3 (Patent Document 4).
The present applicants also have proposed a method for producing a rubber member for a developing roll obtained by applying a coating layer component comprising silicone rubber particles and a binder around a developing roll having a rubber base layer, and curing the coating layer, wherein a reactive silicone oil, an isocyanate compound, and a diluting solvent capable of dissolving both the reactive silicone oil and the isocyanate compound are placed in a reaction vessel, allowed to react in the diluting solvent to perform a prepolymerization reaction while dissolution in the solvent is maintained, then the reaction solution is mixed with a polyol and an isocyanate compound solution, further silicone rubber particles are mixed to prepare a coating liquid of a coating layer component comprising silicone rubber particles and a binder, and the coating liquid is applied around the developing roll and cured (Patent Document 5).